1. Field of the Invention
The field of this invention is valves, and in one aspect, safety valves for regulating flow through rotatable tubular members.
2. Description of the Prior Art
A problem in drilling wells, particularly in emergency situations, is providing safety valves which can block off flow from the well through the rotatable drilling string, kelly and swivel.
Under normal oil well drilling conditions, drilling mud is pumped from the mud pumps at the platform, through the rotating swivel, the rotating kelly, and the rotating drilling string, in order to sweep or wash away cuttings from the drilling bit and return same to the well bore surface in a manner well known. In the event of a sudden increase in downhole pressure, such as from a kick, or when a blowout threatens, flow upwardly through the drilling string and kelly from downhole must be blocked in order to maintain control of the well and prevent drilling mud loss.
Often, valves are mounted above and below the kelly in order to shut off flow through the kelly and the drilling string. However, such valves, sometimes referred to as "kelly cocks", have in the past been ball valves that must be manually rotated to a closed position by a special or other type tool.
Occasionally, it is necessary to close off flow through the kelly under emergency conditions such as, for example, upon the occurrence of an offshore platform fire. In such an emergency situation, it may be impossible for an operator to get close enough to the kelly cock to close the valve and thus the well continues to flow until it can be shut in by other means which can be costly relative to the ecology of the area and costly economically. In addition, under blowout or downhole increased pressure conditions it may be impossible to close the kelly cock because of gases, danger of fire or other causes.